1. Technical Field
The present invention relates to a high power zoom lens system and an image pickup apparatus, and more particularly to a high power zoom lens system suitable for being mounted on a television camera, a video camera, and the like and an image pickup apparatus having the high power zoom lens system.
2. Related Art
Generally, as zoom lens systems mounted on a television camera, a video camera, and the like, zoom lens systems formed of four groups have been known. An exemplary zoom lens system formed of four groups includes in order from an object side: a first lens group having a positive refractive power; a second lens group having a negative refractive power and serving as a zooming group movable for varying power during zooming; a third lens group having a positive or a negative refractive power and correcting image plane variation accompanied by zooming; and a fourth lens group having a positive refractive power.
Meanwhile, zoom lens systems mounted on a television camera and the like demand good operability, a small size with high performance, and a high zoom ratio. To satisfy the demands, zoom lens systems formed of five lens groups have been proposed. For example, Patent Document 1 (Japanese Patent No. 3031598 corresponding to U.S. Pat. No. 5,561,560) describes a zoom lens system that includes in order from an object side: a first lens group having a positive refractive power and remaining stationary during zooming; a second lens group formed of three groups serving as a movable lens group for zooming; a third lens group; a fourth lens group; an aperture diaphragm; and a fifth lens group used for forming an image. The zoom lens system has 17× zoom ratio, and is able to change a space between the third lens group and the fourth lens group to correct variation of comatic aberration accompanied by zooming by interlocking with movement of the second lens group during zooming.
Recently, it has been required that zoom lens systems mounted on a television camera and the like have high power without change of a total length of the optical system. Particularly, it has been further required that the lens systems have high power of 20× magnification. However, as magnifying power increases, aberration variation accompanied by zooming remarkably deteriorates. Thus, it is hard to achieve a high power while satisfying a constraint condition of the total length of the optical system. In addition, it is also hard to obtain high optical performance in the entire range of zooming by suppressing aberration variation accompanied by zooming.
The invention has been made in consideration of the situation mentioned above, and its object is to provide a high power zoom lens system capable of achieving high power without an increase in the total length of the optical system and marinating excellent optical performance by suppressing variation of spherical aberration and comatic aberration during zooming. In addition, it is also an object of the invention to provide an image pickup apparatus having the high power zoom lens system.